This invention relates to pipe flange connections, and more particularly to devices for strengthening the connection between API and other pipe flanges.
In the oil and gas industry API (American Petroleum Institute) flange bolted connections have traditionally been used to fasten several forged body components together for many subsea wellhead and completion systems. As equipment is installed in ever deeper waters, the loads and moments associated with drilling or completion risers grows. Recently, many subsea equipment assemblies have used large diameter high pressure flanges, e.g. a 135/8 inch, 10,000 psi. flange on a 4.times.2, 5000 psi working pressure tree, to withstand the loads and moments. These larger flanges have diameters much larger than what is usually needed for the rest of the forged body, making forgings more costly, weight more, and requiring a special shape.
During design and development of an improved guidelineless subsea completion system, a new problem with conventional API flanges and their connecting bolts was discovered. The design water depth for the system is 1000 meters (3281 ft.), with the possibility of going down further to 1800 meters (5906 ft.). Riser loads due to ocean currents and waves can generate bending moments up to 850,000 ft-lb at the top of the tree and 1.1. million ft-lb at the base of the tree. Analysis of conventional API flanges indicated that the flange bolts fail at these loads, and even oversized API flanges will not meet the task.